Clinical Trials Unit, Department of Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK. email@example.com. Department of Surgery, College of Medicine, University of Ibadan, University College Hospital, Queen Elizabeth Road, Ibadan, 200001, Nigeria. Department of Medicine Unit III, Jinnah Postgraduate Medical Centre, Rafiq Shaheed Road, Karachi, 75510, Pakistan. Clinical Trials Unit, Department of Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK. Rawalpindi Medical University, Holy Family Hospital, Rawalpindi, Pakistan. Department of Cardiovascular Sciences, University of Leicester, Infirmary Square, Leicester, LE1 5WW, UK. Centre for Cancer Prevention, Wolfson Institute of Preventive Medicine, Queen Mary University of London, London, EC1M 6BQ, UK. University of Liverpool, Liverpool, UK. Faculty of Medicine and Health Sciences, University of Nottingham, Queens Medical Centre, Nottingham, NG7 2UH, UK. Division of Gastroenterology, Department of Medicine, University Hospital, Western University, London, Canada. Department of Epidemiology and Biostatistics, Western University, London, ON, Canada. Rawalpindi Medical University and London School of Hygiene and Tropical Medicine (RMU-LSHTM) Collaboration, Room No 294, Holy family Hospital, Said Pur Road, Rawalpindi, Pakistan. Department of Medicine, Services Hospital Unit III, Medical Unit III, Jail Road, Lahore, Pakistan. Transfusion Medicine, NHS Blood and Transplant, Oxford, UK. Department of Haematology, Oxford University Hospitals NHS Foundation Trust, Oxford, UK. Radcliffe Department of Medicine, University of Oxford, and Oxford BRC Haematology Theme, Oxford, UK. Department of Gastroenterology, Royal Wolverhampton NHS Trust, Wolverhampton, UK.